1. Field of the Invention
The present invention relates to a position control system and a velocity control system for controlling movement and positioning of a mechanism having a motor and a load element, and in particular relates to a position control system and a velocity control system suitable for controlling a stage driving mechanism which is driven at least in one axial direction.
2. Description of the Related Art
As this kind of position control system, control systems using a PID control method or a PID and FF control method are known, for example.
As will be described in detail later, in a stage driving mechanism employing a control system of the PID control method or the PID and FF control method, the performance such as a constant velocity and a positioning time may be degraded by the disturbance due to the effect of external unnecessary vibration, motor cogging, and tension of a cable system. In order to suppress the disturbance, a measure to increase a gain of a servo system has been taken. However, when increasing the gain of the servo system, an instability problem of the control system is arisen.
In such situations, the practical point for suppressing the disturbance is measures such as high-grade vibration proof, a high-performance motor with small disturbance and improvement in cable mounting, and improvements in a mechanical system with high accuracy. Such measures, however, increase manufacturing cost.
Accordingly, it is an object of the present invention to provide a position control system for a stage driving mechanism, which is capable of improving performance in a constant velocity and a positioning time by estimating and compensating the disturbance to the system without changing a hardware structure of the system.
It is another object of the present invention to provide a velocity control system for a stage driving mechanism having the performance mentioned above.
The present invention provides a position control system of a stage driving mechanism that drives a stage at least in one-axial direction, and the position control system comprises a position detector for detecting a position of the stage and a feedback control system for controlling a motor, which is a driving source of the stage, on the basis of a detected positional value obtained from the position detector and a positional command value. In accordance with a first aspect of the present invention, the position control system comprises a PID controller for generating a current target value for the motor from the difference between the detected positional value and the positional command value and a disturbance observer. The disturbance observer comprises a signal processing unit for carrying out high-speed calculation according to a predetermined program. The signal processing unit has a filtering function to filter a torque command value for the motor, an input torque estimating and filtering function carrying out estimation for obtaining an estimated input load torque from the detected positional value, and a function to calculate an estimated disturbance load torque from the difference between the filtered torque command value and the estimated input load torque and to generate a correction value for the current target value so as to cancel a disturbance torque on the basis of the estimated disturbance load torque.
A position control system according to a second aspect of the present invention is applied to a stage driving mechanism having a linear motor as a driving source. In this case, the feed back control system comprises the position detector, a first calculator for calculating a first difference between the detected positional value and the positional command value, a PID controller connected to the first calculator for generating a current target value for the linear motor from the first difference, and a motor drive connected to the PID controller for generating a torque command value for the linear motor. The position control system further comprises a second calculator inserted and connected between the PID controller and the motor drive, and a disturbance observer connected to the output side of the second calculator, the output side of the position detector, and one input side of the second calculator. The disturbance observer comprises a signal processing unit for carrying out high-speed calculation according to a predetermined program. The signal processing means comprises a low-pass filter for filtering the torque command value for the linear motor, an input torque estimating filter carrying out estimation for obtaining an estimated input load torque from the detected positional value, a third calculator for calculating a third difference between the filtered torque command value and the estimated input load torque, and an inverse model of a motor torque constant for calculating an estimated disturbance load torque from the third difference and for generating a correction value for the current target value so as to cancel a disturbance torque on the basis of the estimated disturbance load torque calculated above. The second calculator calculates a second difference by subtracting the output value of the inverse model of the motor torque constant from the output value of the PID controller and produces the second difference to the motor drive as a current command value.
The present invention also provides a velocity control system of a stage driving mechanism that drives a stage at least in one-axial direction, and the velocity control system comprises a velocity detector for detecting a velocity of the stage and a feedback control system for controlling a motor, which is a driving source of the stage, on the basis of a detected velocity value obtained from the velocity detector and a velocity command value. In accordance with a third aspect of the present invention, the velocity control system comprises a PID controller for generating a current target value for the motor from the difference between the detected velocity value and the velocity command value and a disturbance observer. The disturbance observer comprises a signal processing unit for carrying out high-speed calculation according to a predetermined program. The signal processing unit has a filtering function to filter a torque command value for the motor, an input torque estimating and filtering function carrying out estimation for obtaining an estimated input load torque from the detected velocity value, and a function to calculate an estimated disturbance load torque from the difference between the filtered torque command value and the estimated input load torque and to generate a correction value for the current target value so as to cancel a disturbance torque on the basis of the estimated disturbance load torque calculated above.
A velocity control system according to a fourth aspect of the present invention is applied to a stage driving mechanism having a linear motor as a driving source. In this case, the feedback control system comprises the velocity detector, a first calculator for calculating a first difference between the detected velocity value and the velocity command value, a PID controller connected to the first calculator for generating a current target value for the linear motor from the first difference, and a motor drive connected to the PID controller for generating a torque command value for the linear motor. The velocity control system further comprises a second calculator inserted and connected between the PID controller and the motor drive and a disturbance observer connected to the output side of the second calculator, the output side of the position detector, and one input side of the second calculator. The disturbance observer comprises a signal processing unit for carrying out high-speed calculation according to a predetermined program. The signal processing unit comprises a filter for filtering the torque command value for the linear motor, an input torque estimating filter carrying out estimation for obtaining an estimated input load torque from the detected velocity value, a third calculator for calculating a third difference between the filtered torque command value and the estimated input load torque, and an inverse model of a motor torque constant for calculating an estimated disturbance load torque from the third difference and for generating a correction value for the current target value so as to cancel a disturbance torque on the basis of the estimated disturbance load torque calculated above. The second calculator calculates a second difference by subtracting the output value of the inverse model of the motor torque constant from the output value of the PID controller and produces the second difference to the motor drive as a current command value.